This invention relates to a roller construction for noncontact guiding of an elongate strip of pliant material, and particularly to such a roller construction capable of pneumatically guiding a web of paper in a rotary printing press without contacting, and so without smearing, the printed surface or surfaces of the web. The noncontact roller according to the invention finds a typical application in a web-fed, multicolor, offset printing press for both pneumatically guiding the web and thermally drying the printed images thereon as the web emerges from a stack of printing units.
A variety of roller constructions have been suggested, and some actually built into rotary printing presses, for drying the images immediately after having been printed on the web or for guiding the printed web without smearing the printings. Japanese Unexamined Patent Publication No. 10-202839 suggests the installation, in a web-fed printing press, of a heating roller and a cooling roller downstream, with respect to the traveling direction of the web, of a printing station in lieu of a more conventional web drying device that consumed large amounts of heated air. The web travels in contact with at least one quarter of the circumference of each such roller. The heating roller has mounted therein a coil, which is to be heated with an alternating current, and is driven at a peripheral speed different from the traveling speed of the web.
An objection to this prior art apparatus is that the traveling web contacts the heating roller and, moreover, rubs against the same as a direct result of the speed difference therebetween. Thus the printing on the web have often not only soiled the web surface but also, the printing ink being so adhesive, adhered to the heating roller. As an additional disadvantage, the drying of the printing by both the heating and cooling has necessitated complex and bulky equipment and also required constant monitoring for temperature control.
Japanese Unexamined Patent Publication No. 11-207928 teaches a noncontact web guide system comprising, in the order of the traveling direction of the web, a hot-air dryer right above a printing station, a noncontact guide roller for horizontally redirecting the web, another noncontact guide roller for further redirecting the web vertically downwardly, and a cooling roller therebelow. All the noncontact guide rollers of this second prior art device are in the form of hollow cylinders of porous material. The rollers are so permeable to air that, fed under pressure into the hollows in the rollers, the air flows through the porous bodies of the rollers and is expelled from all over their surfaces thereby keeping the traveling web out of contact therewith. These rollers are driven at a peripheral speed of not more than half the running speed of the web.
The hot-air dryer and the cooling roller together with the interposed noncontact guide rollers according to this second unexamined patent make up a web guide system of what seems to the instant applicant unnecessarily large space requirement. It is also unjustifiably high in both manufacturing and running costs.
The noncontact guide rollers of porous material are themselves objectionable because of too much waste of pressurized air from those surface portions of the rollers which are left exposed by the web. The curtailment of this waste has been limited, moreover, by the fact that the air pressure has nevertheless had to be sufficiently high to hold the traveling web away from the roller surface. Still further, as the rollers have to be driven at about half the traveling speed of the web, drive linkages have had to be installed at additional costs for rotating the rollers at the required speed.
Japanese Unexamined Patent Publication No. 7-53102 proposes a slightly different noncontact roller, this one being in the form of a hollow cylinder of sintered metal. The roller has a multiplicity of radial pores which are as small in diameter as from ten to thirty micrometers. The web is kept out of contact with the roller surface by the layer of the pressurized air coming out from the pores. The web can be dried by heating the air that is fed under pressure into the roller.
This third prior art device is questionable, however, as to the air that is forced out through that surface portion of the sintered metal roller which is left unembraced by the web. The unexamined patent""s specification merely says on this subject that, preferably, the air should be caused to emit from only that part of the roller surface which is covered by the web, and should be shut off from the rest of the roller surface. No means are disclosed to that end.
Additionally, the sintered metal rollers possess their own drawbacks. They have their metal particles not sufficiently firmly bonded together to withstand use under the most rigorous printing conditions as, for example, in a newspaper printing machine where the roller is required to guide a very wide web running at high speed.
A further weakness of the sintered metal rollers is the filter-like fineness of their pores, which in consequence have been very easy to clog up from within the roller. This weakness has been remedied only by combined use of a large filter system for supplying clean air into the rollers, making the complete guide system even bulkier and more expensive.
The sintered metal rollers have the further yet drawback that, as an inherent result of their method of fabrication, the pores are not uniformly distributed all over the roller surfaces. Thus, with the irregular emission of air from the roller surfaces, the web has been easy to flutter and even contact them, causing the softened ink to stick to the rollers. The sticking ink has indeed been another cause of pore clogging. For all these reasons the sintered metal rollers have necessitated frequent cleaning and replacement and so added significantly to the maintenance costs of the printing press.
Japanese Unexamined Utility Model Publication No. 5-28632 is directed to a nonrotating turnbar for causing a directional change of a web. Tubular in shape, the turnbar has air exit openings formed in its surface portion that is to face the web, for pneumatically holding the web away as in all the references cited above. The unexamined utility model features an air duct disposed on the side of the turnbar opposite to its side facing the web, for supply of additional pressurized air into the space between web and turnbar through nozzles joined to the duct on both upstream and downstream sides of the space.
The teachings of this unexamined utility model are not applicable to guide rollers, however. As an additional disadvantage, two separate passageways are required for supplying pressurized air into the space between web and turnbar, one through the interior, and the other through the exterior, of the turnbar. The resulting air supply system is inordinately bulky and complex.
In view of the foregoing state of the art the present invention has it as an object to provide a noncontact web guide roller assembly of simpler and less expensive construction than the prior art, capable of pneumatically guiding a printed web without smearing the printings or allowing the ink to attach to the roller or other parts and so reducing the waste of paper to a minimum.
Another object of the invention is to provide a noncontact web guide roller assembly of the kind defined, which is adaptable for use with both hot and cold air, for thermally drying and cooling the printed web.
A further object of the invention is to make most effective, wasteless use of the air emitted from the roller for heating, cooling, or simply guiding the web and hence to minimize the operating costs of the roller assembly.
A further object of the invention is to stabilize the posture of the web flying over the roller.
A still further object of the invention is to preclude the clogging of the air exit openings of the roller.
A yet further object of the invention is to make the roller very sturdy in construction and capable of well withstanding use in today""s high-speed newspaper printing press.
Stated broadly in one aspect thereof, the invention concerns a noncontact guide roller assembly comprising a roller in the form of a hollow cylinder defining a plenum chamber therein. The roller has formed in its surface a multiplicity of air outlet openings in communication with the plenum chamber, so that air supplied under pressure to the plenum chamber is expelled from the air outlet openings in order to keep out of contact with the roller a web traveling over circumferential part of the roller surface. The roller assembly also includes baffle means enclosing at least part of the other circumferential part of the roller surface for confining the air being expelled from the openings in the at least part of the other circumferential part of the roller surface and for redirecting the confined air into a pair of spaces, spaced circumferentially of the roller, between the web and the roller.
In use of the roller assembly of the foregoing construction in a web-fed rotary printing press, in a position downstream of a printing station, hot or cold air is to be forced into the plenum chamber within the roller. The air will be expelled under pressure from all over the roller surface, causing the web to fly over certain circumferential part of the roller surface. The roller itself is of very simple mechanical construction and can be made just as sturdy as any other rollers or cylinders currently in use in high-speed newspaper printing presses. The openings in its surface, moreover, need not be so fine as in some prior art devices, requiring no air filtration.
The baffle means, for recovery and reuse of the air escaping from the other circumferential part of the roller surface, is no less simple and strong in construction than the roller, besides being very compact. It is simply a baffle or enclosure, preferably approximately semitubular in shape, defining an air recovery chamber for confining the escaping air. This chamber is open, via openings in a pair of side walls of the baffle which are spaced from each other circumferentially of the roller, to the noted pair of spaces between the web and the roller. The recovered air is therefore redirected into these spaces in order to assure stable web flight over the roller. Thus the air delivered under pressure into the plenum chamber is totally wastelessly utilized for the intended purposes.
Preferably, valve means should be provided for adjustably varying the flow rates of the air through the openings in the baffle side flanges. The valve means adopted in the preferred embodiment are manually operable for independent adjustment of the air pressures in the upstream and downstream side spaces between web and roller in relation to the air pressure supplied directly to the web from the roller surface. Such independent pressure adjustment has proved to lead to unfluttering, nonundulating web flight over the roller.
A further feature of the invention is that the air outlet openings in the roller are inclined upstream, with respect to the prescribed traveling direction of the web, as they extend radially outwardly of the roller. The traveling web will then encounter greater resistance from the airstreams being expelled, and so more easily fly over the roller.
Another aspect of the invention concerns a rotary printing press incorporating one or more noncontact guide roller assemblies of the foregoing construction for drying or simply guiding the web. In a preferred embodiment, in which the invention is applied to a streamlined newspaper printing, cutting, and folding machine, two such roller assemblies are provided in succession, both downstream of the printing station. The upstream roller assembly emits hot air, and the downstream one cold air, for most efficiently drying the printings on the web. The two roller assemblies can be of identical make, the only difference being the temperature of the air supplied thereto.
The above and other objects, features and advantages of this invention and the manner of achieving them will become more apparent, and the invention itself will best be understood, from a study of the following description and attached claims, with reference to the accompanying drawings showing the preferred embodiments of the invention.